56. A widespread terrestrial species becomes divided when rising sea levels isolate a portion of the population on a newly formed island. Genetic analyses show rapid divergence in allele frequencies between mainland and island populations, and after several thousand generations, individuals from the two populations produce inviable hybrids when brought back into contact. Throughout the isolation period, there was no evidence of gene flow between populations. Which evolutionary process is best supported by this scenario?
(A) Introgressive hybridization maintaining genetic connectivity
(B) Behavioral isolation evolving within a continuous population
(C) Instantaneous reproductive isolation caused by genome duplication
(D) Divergence following geographic isolation with interrupted gene flow
(E) Ecological speciation driven by niche differentiation within the same habitat